Dan
Wilson described how the single-ear systems seen in the UK are fitted with
a locking device that prevents any tracking action in rewind. This
uses a sprung pneumatic, powered from the stack supply so that the lock
is removed during play. The lock consists of a bar with a slot that
links with a pin in the tracking pneumatic. When the bar is in place,
the tracking pneumatic cannot move, and the device stays centred.
The photo shows the action fitted to my 65/88 note Pianola pushup, in case
anyone sees fit to make an Aeolian-like locking device for their own machine.

The interesting thing about this is that the locking device was quite
obviously fitted after the machine had been made. Aeolian pushups
mostly seem to have a label stuck in front of where the tracker is fitted
that tells owners about a spare linkage to operate sustaining pedals for
grand pianos. The locking device for the tracker is screwed on top
of this label on all the machines I have seen. The same modification
has been made to all the machines, so it's not a home-made fix.

The conclusion must be that either the UK branch of Aeolian decided
to fit an extra locking device to these machines (which were all made in
the USA but labelled for the destination market), or that American Aeolian
changed the machines between manufacture and shipment.

Perhaps this answers the questions expressed earlier in the MMD about
how the single-ear devices must have worked originally, despite the present-day
problems they present. This modification shows that the devices were
problematic right from the start!